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A003592
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Numbers of the form 2^i*5^j.
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38
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1, 2, 4, 5, 8, 10, 16, 20, 25, 32, 40, 50, 64, 80, 100, 125, 128, 160, 200, 250, 256, 320, 400, 500, 512, 625, 640, 800, 1000, 1024, 1250, 1280, 1600, 2000, 2048, 2500, 2560, 3125, 3200, 4000, 4096, 5000, 5120, 6250, 6400, 8000, 8192, 10000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| These are the natural numbers whose reciprocals are terminating decimals. - David Wasserman (wasserma(AT)spawar.navy.mil), Feb 26 2002
A132726(a(n),k)=0 for k<=a(n); A051626(a(n))=0; A132740(a(n))=1; A132741(a(n))=a(n). - Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Aug 27 2007
Where record values greater than 1 occur in A165706: A165707(n)=A165706(a(n)). [From Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Sep 26 2009]
Also numbers that are divisible by neither 10k-7, 10k-3, 10k-1 nor 10k+1, for all k > 0. [From Robert G. Wilson v (rgwv(AT)rgwv.com), Oct 26 2010]
A204455(5*a(n)) = 5, and only for these numbers. - From Wolfdieter Lang, Feb 04 2012
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LINKS
| R. Zumkeller, Table of n, a(n) for n = 1..1000
Eric Weisstein's World of Mathematics, Regular Number
Eric Weisstein's World of Mathematics, Decimal Expansion
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MATHEMATICA
| fQ[n_] := PowerMod[10, n, n] == 0; Select[ Range@ 10000, fQ] (* Robert G. Wilson v, Jan 12 2012 *)
fQ[n_] := Union[ MemberQ[{1, 3, 7, 9}, # ] & /@ Union@ Mod[ Rest@ Divisors@ n, 10]] == {False}; fQ[1] = True; Select[ Range@ 10000, fQ] [From Robert G. Wilson v (rgwv(AT)rgwv.com), Oct 26 2010]
mx = 14; Sort@ Flatten@ Table[2^i*5^j, {i, 0, mx}, {j, 0, Log[5, 2^(mx - i)]}] (* Or *)
Union@ Flatten@ NestList[{2#, 4#, 5#} &, 1, 7] (* Robert G. Wilson v, Apr 16 2011 *)
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PROG
| (PARI) list(lim)=my(v=List(), N); for(n=0, log(lim)\log(5), N=5^n; while(N<=lim, listput(v, N); N<<=1)); vecsort(Vec(v)) \\ Charles R Greathouse IV, Jun 28 2011
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CROSSREFS
| Sequence in context: A181666 A067943 A067937 * A192716 A159765 A018653
Adjacent sequences: A003589 A003590 A003591 * A003593 A003594 A003595
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KEYWORD
| nonn,changed
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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